Reclaiming rubbers



such copolymer and natural rubber.

Patented Jan. 27, 1953 RECLAIMING RUBBERS George E. P. Smith, Jr., Akron, The Firestone Tire & Rubber Ohio, assignor to Company, Akron,

Ohio, a corporation of Ohio No Drawing. Application March '7, 1949, Serial No. 80,090

2 Claims. 1

The "invention includes improved reclaiming agents as well as the method of reclaiming.

This invention relates to the reclaiming of vulcanizates of rubbery copolymer of styrene and LK-butadiene, and vulcanizates of mixtures of The vulcanizates which can be reclaimed are the vulcanizates which contain combined sulfur. They may be obtained by vulcanizing with sulfur, sulfur halides, polysulfides of phenols or cresols, dialkyl xanthogen sulfides, tetraalkylthiuram sulfides, polysulfides, or other sulfides known to vulcanize chemically unsaturated elastomers. Vulcanization may be effected with or without an accelerator. The invention includes a new reclaiming agent as well as the process of reclaimmg.

Rubbery copolymers of styrene and 1,3-butadiene will be referred to herein by the well-known designation, CTR-S.

According to this invention there is used as the reclaiming agent the sulfide of a relatively highboiling petroleum cresylic acid. In preparing the sulfide the reaction is preferably controlled so as to obtain di cresylic acid) sulfide rather than longer chain compounds. The sulfide produced with sulfur monochloride is preferred to that obtained with sulfur dichloride or other sulfur chloride, but products prepared from all sulfur chlorides are active and are included in the invention, as are the longer chain sulfides.

One method of obtaining petroleum cresylic acid is to extract a cracked petroleum distillate with aqueous caustic soda and thus obtain the salts of the mixture of acids which go to make up the cresylic acids. The resultant solution containing some dissolved oil separates from the distillate by settling. This oil is removed by steam distillation, and the residual solution is acidified to free the cresylic acid which, on standing, rises to the top of the water solution. The acid is then usually recovered by distillation in a vacuum, and it is customary to separate the distillate into fractions of different boiling ranges. These may be further purified, if desired.

Although the composition of the lower boiling petroleum cresylic acids contains roughly the constituents found in the lower boiling cresylic acids obtained from coal-tar and wood-tar, the higher boiling petroleum cresylic acids are of quite different composition from cresylic acids from other sources. For instance, the higher boiling cresylic acids derived from coal-tar contain fused ring compounds. These are not desirable in a reclaiming agent.

As distinguished from the lower boiling cresylic acids, the higher boiling cresylic acids have a relatively high percentage of phenolic materials alkylated with three or more alkyl substituents such as trimethylphenol, tetramethylphenol, dimethylethylphenol, etc. The sulfides from these more highly alkylated phenols are better reclaiming agents than the sulfides from the less highly alkylated phenols. The invention, therefore, relates to the use of sulfides of petroleum cresylic acids of higher boiling range and with a relatively high percentage of phenolic nuclei containing at least three alkyl s'ubstituents. The boiling range may vary but generally a cresylic acid boiling above 220 C. will be used.

In the following table the percentage, composition and boiling range of three dififerent petroleum cresylic acids is given. The expressions C3 alkyl and C4 alkyl are used to refer to the entire content of phenolic materials which contain respectively alkyl substituents totaling three and four carbon atoms, and these are almo'st entirely in the form of methyl and ethyl groups.

Table of cresylic acid compositions Add No. 1

Acid

Percentage composition N O. 3

Percent phenol 1 Percent o-cresoL. Percent n1creso1 Percent p-cresol. Percent xylenols (B. P. 218-225 0 Percent 03 alykl phenols Percent 0 alkyl Initial boiling point Boiling point after distlllation 5 percent phenols.

'50 percent 207 227 percent G 228 240 297 Final boiling point .O 244 300 The preferred cresylic acid for the preparation of sulfides is a petroleum cresylic acid boiling-at 220 C. and higher. It is substantially free from phenol and cresols, and has" no 'more than a relatively small percentage of Xylenols as compared with its content of higher substitutedphenols. It contains a substantial percentage of triand tetra-substituted phenols. The sulfur-monochloride reaction products of acids Nos. 2 and 3 of the preceding table are both reclaiming -agents, whereas the sulfur-monochloride reaction product of acid No. 1 has relatively poor reclaiming properties and its use as such is outside the scope of this invention.

The cresylic acid may be converted to the sulfide in any suitable manner. For example, 160 grams of cresylic acid of the type indicated as acid No. 3 in the preceding table, was dissolved in 640 grams of carbon tetrachloride. The solution was heated to refluxing. Into the boiling solution was dropped slowly with stirring 67 grams of sulfur monochloride. Refiuxin was continued for one hour. The solvent was removed by distillation from a steam bath, with the aid of a stream of air at the end of the distillation. The ratio of acid to sulfur chloride will vary with the equivalent weight of the acid. Thus, for the type of acid designated as acid No. 2 in the foregoing table, only 140 grams is recommended for reaction with 67 grams of sulfur monochloride, as above described.

The reclaiming process is illustrated by the following example. The GR-S scrap of Examples 1 and 2, and the recap peels of Example 3, all contained combined sulfur.

EXAMPLE 1 In evaluating the sulfide prepared with acid No. 2 of the above table, GR-S scrap was reclaimed according to the following formula:

. Parts by weight GR-S tread scrap mesh) 200 Solvent (dipentene fraction boiling at 173 to 201 C.) 12 Coumarone-indene resin 12 Reclaiming agent 3 The solvent, resin, and reclaiming agent were heated together gently until solution was obtained, and then incorporated into the scrap by use of a laboratory mixer. After mixing, the scraps were aged for at least six hours before the reclaiming operation. The heating was carried out in a laboratory pan heater; the treated scrap was subjected to open steam of 175 pounds pressure per square inch for four hours. After completion of the heating period, factory vacuum was applied to the stock for a period of one hour to insure dryness. The softened scrap mass in biscuit form was then removed from the heater and allowed to cool to room temperature. The softened biscuit from the heating operation was removed from the pan, blended, and massed by four passes through an open laboratory mill, to insure uniformity. A portion of each reclaim weighing about 50 grams was then refined by three passes on a cool laboratory mill at about 110 F. This mill was equipped with a refiner knife and was tightened to the proper setting, so that a thickness of 0.005 inch was obtained wlilesn a piece of solder was passed between the re The reclaims may be evaluated by the thickness of a sheet produced under such a setting of the refiner knife, by manual evaluation of the body and tack, and by determination of the Mooney plasticity of the refined reclaim. The sheet thickness may be taken as a measure of the softness of the reclaim.

The body rating is a manual evaluation of the stretch and elongation, and also the appearance and uniformity of the stretched sheet. Body is rated on a scale in which 6, the top rating, represents a very good sheet, and the bottom rating of A; represents a very poor lacy or tough sheet.

On this scale a rating of 4% is fair, and 3 /2 is poor to fair. Sheets with a rating of 4 or better are, in general, commercially satisfactory. The top rating of 6 is seldom achieved.

Tack is the tendency of a sheet of reclaim to adhere to itself. It was determined by laying a sheet of reclaim in the palm of one hand, and then pressing the thumb and first finger of the hand together. On subsequently spreading the thumb and first finger, a small but definite force was required to separate the two adhering surfaces. Ratings were arbitrarily assigned as follows: 10 to milled crude rubber, 5 to a sheet of typical natural-rubber whole-tire reclaim, and 0 to crude GR-S with no tack. Values from 1 to 10, on this arbitrary scale, were assigned by the observer. Reclaimed GR-S with a tack rating of 4 0r 5 is generally commercial.

The over-all evaluation is often referred to in the industry as the workability of the reclaim. This can largely be determined from a consideration of the sheet thickness, body, and tack, determined as indicated. The so-called quality index which is the sum of the values for the body and tack is a relatively accurate guide to the workability of the reclaim. To meet commercial requirements a reclaim having a quality index of at least 7 or 8 is in general required.

The evaluation of the GRr-S vulcanizate reclaims prepared with sulfide from acid No. 2 of the above table of cresylic acid compositions, compared to GR-S reclaim similarly prepared with sulfide from acid No. 1, as described, is recorded below:

GR-S Reclaimed witli Acid No. 2 Sulfide Acid No. l Sulfide Thickness Ta ck Quality Index The reclaim from GR-S using the sulfide from acid No. 2 is shown to be definitely better than the reclaim obtained with acid No. l sulfide.

EXAMPLE 2 Cresylic acid sulfides prepared from acids No. 1 and 3 more particularly defined in the foregoing table of cresylic acid compositions were added to the respective compositions. Two separate batches of GR-S scrap were treated respectively with these reclaiming compositions. The mixtures of scrap and reclaiming compositions were cooked four hours at pounds steam pressure. The resulting products were given three passes through the laboratory refining mill. The products were tested and the results are recorded in the following table, the different products be ing identified by reference to the respective rcclaiming agents used in producing them.

Properties of reclaims The reclaim obtained by the use of the sulfide of acid No. 3 is commercially acceptable whereas that obtained with the sulfide of acid No. 1 is not.

Undetermined differences in handling and processing gave reclaims which, compared with those of the preceding example, are drier and stiffer. In spite of this unexplained variation, the differences between the two products of this example, similarly obtained, are significant.

The differences in the reclaiming values of the sulfides of these acids is such that commercially the sulfide of acid No. 3 is satisfactory whereas the sulfide of acid No. 1 is not. The differences in the laboratory results in any one run are indicative of results which are obtained uniformly in the reclaiming plant.

ESCANIPLE 3 No. 1 passenger recap peels (containing a mixture of natural-rubber vulcanizate and GR-S vulcanizate) were ground to 14 mesh. One hundred parts by weight were treated with a solution obtained by heating the following:

Parts by weight Solvent 6.67 Wood resin 3.33 Crescylic acid No. 2 sulfide .4 Insecticide oil 1 The ground peels were treated with the resulting mix during a warming-up period of one minute at 406 F., and then for one minute at 512 F. The solvent is a commercial solvent which is a coal-tar naphtha oil containing unsaturated resins, having a boiling point of 187-34'7 C, and a specific gravity of 1.06-1.09. The insecticide oil is a neutral petroleum oil with a boiling point of 192-256 C. and a specific gravity of 0.78.

The vulcanizate was thoroughly and uniformly devulcanized and the reclaim was of standard quality.

The novelty of the process lies in the use of the cresylic acid sulfide and the beneficial results obtained from its use. The usual equipment-may be used. Usual temperatures and times of treatment may be employed ranging from twenty hours at 300 F. to one minute at 600 F., or thereabouts. The reclaiming composition will include in addition to the cresylic acid sulfide, swelling agent and tackifier. Dipentene may be used as swelling agent, as in Example 1, or coal-tar naphtha as in Example 3. The liquid resin of Example 2 is a swelling agent which also has tackifying properties. Other commonly used swelling agents may be employed, such as pine tar oil, petroleum naphtha, turpentine, cymene, etc. The tackifier may be a coumaronaindene, or coumarone-indene resin, as in Example 1. It may be wood resin, as in Examples 2 and 3. Other tackifiers may be employed such as rosin oil, pine tar, etc.

The above examples are illustrative.

What I claim is:

1. Sulfide of a petroleum cresylic acid, which acid has a boiling range above 220 C., is substantially free from unalkylated phenol and cresols, and contains a substantially higher percentage of phenols containing at least three alkyl substituents than its percentage content of dialkylated phenols, said alkyl substituents being almost entirely in the form of methyl and ethyl groups.

2. The method of reclaiming vulcanizate of rubbery copolymer of 1,3-butadiene and styrene which contains combined sulfur, which comprises rendering the vulcanizate plastic by heating the vulcanizate at a temperature in the range of about 300 F. to about 600 F. with a swelling agent, a tackifier and a sulfide as defined in claim 1.

GEORGE? E. P. SMITH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,359,122. Kirby et a1 Sept. 26, 1944 2,372,584 Kirby et al Mar. 27, 1945 2,402,448 Richards June 18, 1946 2,449,026 Van Gilder Sept. 7, 1948 2,469,529 Tewksbury et al. May 10, 1949 FOREIGN PATENTS Number Country Date 610,901 Great Britain 1948 OTHER REFERENCES Rubber Age, May 1947, page 204. Cook et al., Ind. and Eng. Chem., pages 1194- 1203, July 1948. 

1. SULFIDE OF A PETROLEUM CRESYLIC ACID, WHICH ACID HAS A BOILING RANGE ABOVE 220* C., IS SUBSTANTIALLY FREE FROM ALKYLATED PHENOL AND CRESOLS, AND CONTAINS A SUBSTANTIALLY HIGHER PERCENTAGE OF PHENOLS CONTAINING AT LEAST THREE ALKYL SUBSTITUENTS THAN ITS PERCENTAGE CONTENT OF DIALKYLATED PHENOLS, SAID ALKYL SUBSTITUENTS BEING ALMOST ENTIRELY IN THE FORM OF METHYL AND ETHYL GROUPS.
 2. THE METHOD OF RECLAIMING VULCANIZATE OF RUBBERY COPOLYMER OF 1,3-BUTADIENE AND STYRENE WHICH CONTAINS COMBINED SULFUR, WHICH COMPRISES RENDERING THE VULCANIZATE PLASTIC BY HEATING THE VULCANIZATE AT A TEMPERATURE IN THE RANGE OF ABOUT 300* C. TO ABOUT 600* F. WITH A SWELLING AGENT. A TACKIFIER AND A SULFIDE AS DEFINED IN CLAIM
 1. 